Compressor oil recovering apparatus and multi-unit air conditioner equiped with the same

ABSTRACT

A multi-unit air conditioner is disclosed. The multi-unit air conditioner includes an outdoor unit comprising at least two compressors, a plurality of indoor units connected to the outdoor unit, a plurality of oil separators each connected to an associated one of the compressors to separate oil from a refrigerant discharged from the associated compressor, an oil storage for storing the oil separated from each oil separator, a plurality of oil supplying tubes each having one end connected to the oil storage, and the other end connected to an associated one of the compressors to supply the oil stored in the oil storage to the associated compressor, and adjusters each arranged at an associated one of the oil supplying tubes to adjust an amount of oil supplied from the oil storage to an associated one of the compressors in accordance with an oil storage state of the associated compressor.

This application claims the benefit of Korean Patent Application No.P2004-94623, filed on Nov. 18, 2004 which is hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an air conditioner, and more particularly, to a compressor oil recovering apparatus for a multi-unit air conditioner.

2. Discussion of the Related Art

Generally, air conditioners perform procedures of compressing, condensing, expanding and evaporating a refrigerant to cool and/or heat a confined space. Such air conditioners are classified into a cooling type wherein a refrigerant flows only in one direction through a refrigerant cycle, to supply cold air to a confined space, and a cooling and heating type wherein a refrigerant flows bi-directionally in a selective manner through a refrigerant cycle, to selectively supply cold air or hot air to a confined space.

Also, such air conditioners are classified into a general type wherein one indoor unit is connected to one outdoor unit, and a multi-unit type wherein a plurality of indoor units are connected to one outdoor unit. For the multi-unit type, an air conditioner may be implemented which includes at least one outdoor unit.

Meanwhile, the outdoor unit of such a multi-unit air conditioner includes at least one compressor corresponding to the load of the indoor units, and an oil separator connected to a refrigerant discharge line of the compressor, and adapted to separate oil from a refrigerant discharged from the compressor.

The compressor sucks low-temperature and low-pressure refrigerant gas, compresses the sucked refrigerant gas into high-temperature and high-pressure refrigerant gas, and discharges the resulting refrigerant gas. When such high-temperature and high-pressure refrigerant gas is discharged from the compressor, oil present in the compressor is also discharged together with the refrigerant. The oil contained in the discharged refrigerant is again fed to the compressor after being separated from the refrigerant in the oil separator.

In the conventional multi-unit air conditioner, however, a problem occurs when the oil separated by the oil separator is returned to the compressor via a refrigerant suction line.

That is, the oil separated by the oil separator may be re-discharged together with the refrigerant discharged from the compressor via the refrigerant discharge line, without being returned to the compressor via the refrigerant suction line. This is because there is a pressure difference between the refrigerant suction line and the refrigerant discharge line due to the flow rate of the refrigerant discharged through the refrigerant discharge line. As a result, shortage of oil may occur in the compressor.

Such oil shortage may cause abrasion and performance degradation of the compressor. As a result, the compressor exhibits a degradation in reliability.

The performance degradation of the compressor results in a degradation in the efficiency of the multi-unit air conditioner using the compressor, thereby causing a degradation in cooling/heating performance.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a compressor oil recovering apparatus and a multi-unit air conditioner equipped with the same that substantially obviate one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a multi-unit air conditioner which includes a compressor oil recovering apparatus capable of effectively recovering oil, using a simple configuration.

Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a compressor oil recovering apparatus comprises: a plurality of oil separators respectively connected to a plurality of compressors, each of the oil separators separating oil from a refrigerant discharged from an associated one of the compressors; an oil storage for storing the oil separated from each of the oil separators; and a plurality of oil supplying tubes each having one end connected to the oil storage, and the other end connected to an associated one of the compressors, each of the oil supplying tubes supplying the oil stored in the oil storage to the associated compressor.

The compressor oil recovering apparatus may further comprise adjusters each arranged at an associated one of the oil supplying tubes, and adapted to adjust an amount of oil supplied from the oil storage to an associated one of the compressors in accordance with an oil storage state of the associated compressor.

Each of the adjusters may comprise a float arranged in an associated one of the compressors, and adapted to sense a level of oil stored in the associated compressor, and a float valve for controlling supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil level.

The float valve may be arranged at a position where an associated one of the oil supplying tubes is connected to the associated compressor.

Each of the adjusters may comprise an oil sensor adapted to sense an amount of oil stored in an associated one of the compressors, and a solenoid valve adapted to control supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil amount.

The oil sensor may be arranged in the associated compressor.

The solenoid valve may be arranged at a position where an associated one of the oil supplying tubes is connected with the associated compressor.

The compressor oil recovering apparatus may further comprise strainers respectively arranged at the oil supplying tubes, and adapted to filter the oil supplied to the compressors to remove foreign matter contained in the oil.

The oil storage may be connected with the oil separators by a plurality of oil recovering tubes, respectively.

At least one of the compressors may comprise a variable-capacity compressor.

In another aspect of the present invention, a multi-unit air conditioner comprises: an outdoor unit comprising a plurality of compressors, and an outdoor heat exchanger; a plurality of indoor units connected to the outdoor unit, each of the indoor units comprising an indoor heat exchanger; a plurality of oil separators respectively connected to the compressors, each of the oil separators separating oil from a refrigerant discharged from an associated one of the compressors; an oil storage for storing the oil separated from each of the oil separators; and a plurality of oil supplying tubes each having one end connected to the oil storage, and the other end connected to an associated one of the compressors, each of the oil supplying tubes supplying the oil stored in the oil storage to the associated compressor.

The indoor units may be connected to the outdoor unit by a refrigerant line.

The multi-unit air conditioner may further comprise indoor fans each arranged in an associated one of the indoor units, and adapted to suck air from a confined space into the associated indoor unit, and then to discharge the air from the associated indoor unit to the confined space.

The multi-unit conditioner may further comprise an outdoor fan arranged in the outdoor unit, and adapted to suck outdoor air into the outdoor unit, and then to discharge the air from the outdoor unit to the atmosphere.

The multi-unit air conditioner may further comprise adjusters each arranged at an associated one of the oil supplying tubes, and adapted to adjust an amount of oil supplied from the oil storage to an associated one of the compressors in accordance with an oil storage state of the associated compressor.

Each of the adjusters may comprise a float arranged in an associated one of the compressors, and adapted to sense a level of oil stored in the associated compressor, and a float valve for controlling supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil level.

The float valve may be arranged at a position where an associated one of the oil supplying tubes is connected with the associated compressor.

Each of the adjusters may comprise an oil sensor adapted to sense an amount of oil stored in an associated one of the compressors, and a solenoid valve adapted to control supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil amount.

The oil sensor may be arranged in the associated compressor. The solenoid valve may be arranged at a position where an associated one of the oil supplying tubes is connected with the associated compressor.

The multi-unit air conditioner may further comprise strainers respectively arranged at the oil supplying tubes, and adapted to filter the oil supplied to the compressors to remove foreign matter contained in the oil.

The oil storage may be connected with the oil separators by a plurality of oil recovering tubes, respectively.

The oil storage may comprise a storing container in which a single storing chamber is defined.

At least one of the compressors may comprise a variable-capacity compressor.

In another aspect of the present invention, a multi-unit air conditioner comprises: an outdoor unit comprising at least two compressors; a plurality of indoor units connected to the outdoor unit; a plurality of oil separators respectively connected to the compressors, each of the oil separators separating oil from a refrigerant discharged from an associated one of the compressors; an oil storage for storing the oil separated from each of the oil separators; a plurality of oil supplying tubes each having one end connected to the oil storage, and the other end connected to an associated one of the compressors, each of the oil supplying tubes supplying the oil stored in the oil storage to the associated compressor; and adjusters each arranged at an associated one of the oil supplying tubes, and adapted to adjust an amount of oil supplied from the oil storage to an associated one of the compressors in accordance with an oil storage state of the associated compressor.

It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:

FIG. 1 is a partially-broken perspective view illustrating a multi-unit air conditioner according to a first embodiment of the present invention;

FIG. 2 is a schematic view illustrating a refrigerant cycle established during a cooling operation of the multi-unit air conditioner shown in FIG. 1;

FIG. 3 is a schematic view illustrating a compressor oil recovering apparatus shown in FIG. 2; and

FIG. 4 is a schematic view illustrating a compressor oil recovering apparatus according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

FIGS. 1 to 3 illustrate a multi-unit air conditioner according to a first embodiment of the present invention. This multi-unit air conditioner will be described with reference to FIGS. 1 to 3.

FIG. 1 is a partially-broken perspective view illustrating the multi-unit air conditioner according to the first embodiment of the present invention. FIG. 2 is a schematic view illustrating a refrigerant cycle established during a cooling operation of the multi-unit air conditioner shown in FIG. 1. FIG. 3 is a schematic view illustrating a compressor oil recovering apparatus shown in FIG. 2.

As shown in FIGS. 1 and 2, the multi-unit air conditioner according to the first embodiment of the present invention includes an outdoor unit 80, and a plurality of indoor units 51, 52, 53, and 54. The multi-unit air conditioner also includes a refrigerant line 100 for connecting the indoor units 51, 52, 53, and 54 to the outdoor unit 80.

The refrigerant line 100 includes a first refrigerant line 110 connected to a receiver 87 c included in the outdoor unit 80 at one end of the first refrigerant line 110, and branched into a plurality of branch lines 111, 112, 113, and 114 at the other end of the refrigerant line 110 such that the refrigerant line 110 is connected to one end of each of the indoor units 51, 52, 53, and 54 via an associated one of the branch lines 111, 112, 113, and 114. The refrigerant line 100 also includes a second refrigerant line 120 connected to an accumulator 87 a included in the outdoor unit 80 at one end of the second refrigerant line 120, and branched into a plurality of branch lines 121, 122, 123, and 124 at the other end of the refrigerant line 120 such that the refrigerant line 120 is connected to the other end of each of the indoor units 51, 52, 53, and 54 via an associated one of the branch lines 121, 122, 123, and 124.

Accordingly, a refrigerant is introduced into the indoor units 51, 52, 53, and 54 through the first refrigerant line 110. Flows of the refrigerant respectively emerging from the indoor units 51, 52, 53, and 54 are joined through the second refrigerant line 120 which, in turn, supplies the refrigerant to the outdoor unit 80.

Each of the indoor units 51, 52, 53, and 54 includes an indoor fan 74 adapted to force indoor air in a confined space to be sucked into the associated indoor unit 51, 52, 53, or 54, and then to be discharged into the confined space. Each indoor unit 51, 52, 53, or 54 also includes an indoor heat exchanger 72 adapted to cause the indoor air sucked into the associated indoor unit 51, 52, 53, or 54 to heat-exchange with the refrigerant such that the indoor air is cooled or heated.

The outdoor unit 80 includes an outdoor fan 81 adapted to force outdoor air to be sucked into the outdoor unit 80, and then to be discharged into the atmosphere, and an outdoor heat exchanger 82 adapted to cause the outdoor air sucked into the outdoor unit 80 by the outdoor fan 81 to heat-exchange with the refrigerant. The outdoor unit 80 also includes a plurality of compressors 83 and 84, each adapted to compress the refrigerant, and a plurality of oil separators 85 and 86 connected to refrigerant discharge lines 83 a and 84 a extending from the compressors 83 and 84, and adapted to separate oil from the refrigerant discharged from the compressors 83 and 84, respectively.

Although not shown, each of the compressors 83 and 84 includes a compressing section having a compressing chamber, in which the refrigerant is compressed, a motor section for reducing the volume of the compressing chamber for the compression of the refrigerant, and an oil pump for pumping oil for lubrication of the motor section or compressing section.

At least one of the compressors 83 and 84 is of a variable capacity type, and the remaining one or ones of the compressors 83 and 84 are of a constant-speed type. In the illustrated case, the compressor 83 is of the variable capacity type, and the compressor 84 is of the constant-speed type. When the load to be processed by the indoor units 51, 52, 53, and 54 (hereinafter, referred to as a “indoor unit load”) is small, for example, when only one or two of the indoor units 51, 52, 53, and 54 operate, only the variable-capacity compressor 83 is driven to cope with the indoor unit load. On the other hand, in the case of a large indoor unit load, for example, when three or more of the indoor units 51, 52, 53, and 54 operate, it is desired to operate not only the variable-capacity compressor 83, but also the constant-speed compressor 84.

The multi-unit air conditioner according to the first embodiment of the present invention further includes a common accumulator 87 a arranged in the outdoor unit 80 while being connected to respective refrigerant suction line 83 b and 84 b of the variable-capacity compressor 83 and constant-speed compressor 84. The common accumulator 87 a accumulates refrigerant liquid so that only refrigerant gas is introduced into the variable-capacity compressor 83 and constant-speed compressor 84.

The multi-unit air conditioner according to the first embodiment of the present invention further includes a 4-way valve 87 b arranged in the outdoor unit 80 to change the path of the refrigerant such that the refrigerant emerging from the oil separators 85 and 86 is selectively introduced into the indoor heat exchangers 72 or into the outdoor heat exchanger 82, thereby enabling the indoor units 51, 52, 53, and 54 to be used as coolers or heaters.

The receiver 87 c arranged in the outdoor unit 80 is also included in the multi-unit air conditioner according to the first embodiment of the present invention. The receiver 87 c not only stores a surplus of refrigerant, but also causes only refrigerant liquid to be circulated through the indoor units during the cooling operation.

The multi-unit air conditioner according to the first embodiment of the present invention further includes an orifice or electronic expansion valve 88 a arranged at the refrigerant line 100 between the outdoor heat exchanger 82 and each of the indoor heat exchangers 72, and adapted to expand the refrigerant emerging from the outdoor heat exchanger 82 and the associated indoor heat exchanger 72 into a low-temperature and low-pressure state. The multi-unit air conditioner also includes an electronic expansion valve 88 b arranged in the outdoor unit 80, and adapted to control the flow rate of the refrigerant circulating through the outdoor unit 80, and thus, the refrigerant cycle.

The multi-unit air conditioner according to the first embodiment of the present invention further includes check valves 89 respectively arranged in the refrigerant discharge lines 83 a and 84 a of the variable-capacity compressor 83 and constant-speed compressor 84.

Meanwhile, as shown in FIGS. 2 and 3, the multi-unit air conditioner further includes a compressor oil recovering apparatus. The compressor oil recovering apparatus includes an oil storage 151 for receiving and storing oil separated from the oil separators 85 and 86, and a plurality of oil supplying tubes 153 and 154 each connected between the oil storage 151 and an associated one of the compressors 83 and 84 to supply the oil stored in the oil storage 151 to the associated compressor 83 or 84.

The oil storage 151 may be a storing container defined with a single storing chamber therein. The oil storage 151 is connected to the plural separators 85 and 86 via a plurality of oil recovering tubes 156 and 157, respectively.

The compressor oil recovering apparatus further includes adjusters each arranged for adjusting the amount of oil supplied from the oil storage 151 to an associated one of the compressors 83 and 84 in accordance with the oil storage state of the associated compressor 83 or 84.

As shown in FIG. 3, each adjuster includes a float 159 a adapted to sense the level of the surface of oil stored in the associated compressor 83 or 84. Each adjuster also includes a float valve 159 for controlling the supply or cut-off of the oil supplied to the associated compressor 83 or 84, and the amount of the supplied oil in accordance with the oil surface level sensed by the float 159 a.

It is preferred that the float valve 159 be arranged at an end of an associated one of the oil supply tubes 153 and 154 arranged adjacent to the associated compressor 83 or 84.

The compressor oil recovering apparatus further includes strainers 153 a and 154 a respectively arranged at the oil supplying tubes 153 and 154, and adapted to filter the oil supplied to the compressors 83 and 84 to remove foreign matter contained in the oil.

Hereinafter, a procedure for recovering the compressor oil in the multi-unit air conditioner having the above-described configuration according to the illustrated embodiment of the present invention will be described.

When the refrigerant emerging from the compressors 83 and 84 passes through the 4-way valve 87 b to be circulated through the outdoor heat exchanger 82, expansion device 88 a, and indoor heat exchangers 72, in this order, a cooling cycle is established to cause the indoor units 51, 52, 53, and 54 to operate in cooling mode. When the refrigerant circulates in a direction reverse to that of the cooling mode in accordance with the change of the refrigerant flow by the 4-way valve 87 b, a heating cycle is established to operate the indoor units 51, 52, 53, and 54 in heating mode. The following description will be given only in conjunction with the case in which the multi-unit air conditioner establishes the cooling cycle.

First, when the multi-unit air conditioner operates such that a part of the indoor units 51, 52, 53, and 54, for example, one or two of the indoor units 51, 52, 53, and 54, operates in cooling mode, only the variable-capacity compressor 83 of the outdoor unit 80 operates. In this case, the constant-speed compressor 83 of the outdoor unit 80 does not operate.

Accordingly, the variable-capacity compressor 83 compresses the refrigerant into a high-temperature and high-pressure state, and then discharges the compressed refrigerant through the refrigerant discharge line 83 a together with oil. A large part of the oil discharged together with the refrigerant is separated from the refrigerant while passing through the oil separator 85. The remaining oil is circulated through the refrigerant cycle, together with the refrigerant.

The refrigerant emerging from the oil separator 85 is introduced into the indoor heat exchanger or indoor heat exchangers 72 of the indoor unit or indoor units, which operate in cooling mode, after passing through the 4-way valve 87 b, outdoor heat exchanger 82, and expansion device or expansion devices 88 a, in this order. The refrigerant is then evaporated while cooling air present around the indoor heat exchanger or indoor heat exchangers 72, thereby causing the indoor unit or indoor units to function as a cooler or coolers. The refrigerant is subsequently returned to the variable-capacity compressor 83.

Meanwhile, the oil separated from the refrigerant in the oil separator 85 is fed to the oil storage 151 through the oil recovering tube 156, and is stored in the oil storage 151. Subsequently, the stored oil is directly re-supplied to the variable-capacity compressor 83 through the oil supplying tube 153.

The supply or cut-off of the oil supplied to the variable-capacity compressor 83 and the flow rate of the supplied oil are controlled by the float valve 159 arranged at the oil supplying tube 153 in accordance with the oil storage state of the variable-capacity compressor 83.

Thus, in the multi-unit air conditioner according to the illustrated embodiment of the present invention, the oil separated from the refrigerant by the oil separator 85 is directly supplied to the variable-capacity compressor 83 through the oil storage 151 and oil supplying tube 153, contrary to the conventional case in which the separated oil is supplied to the variable-capacity compressor 83 through the refrigerant suction line 83 b. Accordingly, it is possible to prevent shortage of oil from occurring in the variable-capacity compressor 83.

Meanwhile, when the variable-capacity compressor 83 operates for a prolonged period of time, the oil present in the cooling cycle is concentrated in the variable-capacity compressor 83. As a result, non-uniform oil distribution occurs between the compressors 83 and 84.

In the multi-unit air conditioner according to the illustrated embodiment of the present invention, such non-uniform oil distribution is prevented by the oil storage 151 connected with the oil separators 85 and 86, the oil supplying tubes 153 and 154, which supply the oil stored in the oil storage 151 to the compressors 83 and 84, and the float valve 159, which controls the oil supplied to the compressors 83 and 84 via the oil supplying tubes 153 and 154.

That is, the float valve 159 senses the surface level of oil corresponding to the minimum oil amount of each of the compressors 83 and 84. Based on the sensed oil surface level, the oil stored in the oil storage 151 is supplied to the compressor 83 or 84, in which shortage of oil has occurred. Accordingly, it is possible to prevent non-uniform oil distribution between the compressors 83 and 84.

Since oil is supplied to the compressor 83 or 84, in which shortage of oil has occurred, immediately at the point of time when non-uniform oil distribution between the compressors 83 and 84 occurs, it is possible to achieve an enhancement in the performance of the compressors 83 and 84, and thus, the efficiency of the multi-unit air conditioner.

FIG. 4 is a schematic view illustrating a compressor oil recovering apparatus according to a second embodiment of the present invention.

Referring to FIG. 4, the compressor oil recovering apparatus, which is included in a multi-unit air conditioner according to the second embodiment of the present invention, includes oil sensors 259 a each arranged in an associated one of the compressors 83 and 84, and adapted to sense the amount of oil stored in the associated compressor 83 or 84. The compressor oil recovering apparatus also includes solenoid valves 259 each adapted to control the supply or cut-off of the oil supplied to an associated one of the compressor 83 and 84, and the amount of the supplied oil in accordance with the oil amount sensed by an associated one of the oil sensors 259 a.

In this case, the oil sensors 259 a substitute for the floats 159 described in the first embodiment, and the solenoid valves 259 substitute for the float valves 159 of the first embodiment. The oil sensors 259 a and solenoid valves 259 perform functions similar to those of the first embodiment.

Each solenoid valve 259 may be arranged at a position where an associated one of the oil supplying tubes 153 and 154 is connected with an associated one of the compressors 83 and 84.

In accordance with the second embodiment of the present invention, the multi-unit air conditioner also includes strainers 153 a and 154 a respectively arranged at the oil supplying tubes 153 and 154, and adapted to filter the oil supplied to the compressors 83 and 84 to remove foreign matter contained in the oil.

In the multi-unit air conditioner according to the illustrated embodiment of the present invention, each solenoid valve 259 is controlled, based on the amount of oil sensed by the float valve 159 arranged in the associated compressor 83 or 84. Based on the sensed oil amount, an amount of oil required in the associated compressor 83 or 84 is supplied to the associated compressor 83 or 84. Accordingly, it is possible to prevent oil shortage and non-uniform oil distribution from occurring during the operation of the compressors 83 and 84.

The multi-unit air conditioner according to the present invention, which has been described, has various effects.

First, in accordance with the present invention, the oil, which is separated from the refrigerant in the oil separators, is smoothly supplied to the oil storing section of each compressor. Accordingly, there are advantages of preventing abrasion and noise from being generated in the compressors, increasing the life of the compressors, and enhancing the system efficiency of the air conditioner.

Second, in accordance with the present invention, the oil discharged from each compressor together with the refrigerant is recovered to the compressor via a single oil path defined by the oil separator, oil recovering tube, oil storage, and oil supplying tube. Accordingly, there is an advantage in that it is possible to efficiently recover compressor oil.

Third, in accordance with the present invention, it is possible to continuously supply an appropriate amount of oil, based on the oil storage state of each compressor. Accordingly, it is possible to prevent oil shortage in the compressors, and non-uniform oil distribution between the compressors, and thus, to achieve an enhancement in the performance of the compressors.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. 

1. A compressor oil recovering apparatus comprising: a plurality of oil separators respectively connected to a plurality of compressors, each of the oil separators separating oil from a refrigerant discharged from an associated one of the compressors; an oil storage for storing the oil separated from each of the oil separators; and a plurality of oil supplying tubes each having one end connected to the oil storage, and the other end connected to an associated one of the compressors, each of the oil supplying tubes supplying the oil stored in the oil storage to the associated compressor.
 2. The compressor oil recovering apparatus according to claim 1, further comprising: adjusters each arranged at an associated one of the oil supplying tubes, and adapted to adjust an amount of oil supplied from the oil storage to an associated one of the compressors in accordance with an oil storage state of the associated compressor.
 3. The compressor oil recovering apparatus according to claim 2, wherein each of the adjusters comprises: a float arranged in an associated one of the compressors, and adapted to sense a level of oil stored in the associated compressor; and a float valve for controlling supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil level.
 4. The compressor oil recovering apparatus according to claim 3, wherein the float valve is arranged at a position where an associated one of the oil supplying tubes is connected to the associated compressor.
 5. The compressor oil recovering apparatus according to claim 2, wherein each of the adjusters comprises: an oil sensor adapted to sense an amount of oil stored in an associated one of the compressors; and a solenoid valve adapted to control supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil amount.
 6. The compressor oil recovering apparatus according to claim 5, wherein the oil sensor is arranged in the associated compressor.
 7. The compressor oil recovering apparatus according to claim 5, wherein the solenoid valve is arranged at a position where an associated one of the oil supplying tubes is connected with the associated compressor.
 8. The compressor oil recovering apparatus according to claim 1, further comprising: strainers respectively arranged at the oil supplying tubes, and adapted to filter the oil supplied to the compressors to remove foreign matter contained in the oil.
 9. The compressor oil recovering apparatus according to claim 1, wherein the oil storage is connected with the oil separators by a plurality of oil recovering tubes, respectively.
 10. The compressor oil recovering apparatus according to claim 5, wherein at least one of the compressors comprises a variable-capacity compressor.
 11. A multi-unit air conditioner comprising: an outdoor unit comprising a plurality of compressors, and an outdoor heat exchanger; a plurality of indoor units connected to the outdoor unit, each of the indoor units comprising an indoor heat exchanger; a plurality of oil separators respectively connected to the compressors, each of the oil separators separating oil from a refrigerant discharged from an associated one of the compressors; an oil storage for storing the oil separated from each of the oil separators; and a plurality of oil supplying tubes each having one end connected to the oil storage, and the other end connected to an associated one of the compressors, each of the oil supplying tubes supplying the oil stored in the oil storage to the associated compressor.
 12. The multi-unit air conditioner according to claim 11, further comprising: an outdoor fan arranged in the outdoor unit, and adapted to suck outdoor air into the outdoor unit, and then to discharge the air from the outdoor unit to the atmosphere; and indoor fans each arranged in an associated one of the indoor units, and adapted to suck air from a confined space into the associated indoor unit, and then to discharge the air from the associated indoor unit to the confined space.
 13. The multi-unit air conditioner according to claim 11, further comprising: adjusters each arranged at an associated one of the oil supplying tubes, and adapted to adjust an amount of oil supplied from the oil storage to an associated one of the compressors in accordance with an oil storage state of the associated compressor.
 14. The multi-unit air conditioner according to claim 13, wherein each of the adjusters comprises: a float arranged in an associated one of the compressors, and adapted to sense a level of oil stored in the associated compressor; and a float valve for controlling supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil level.
 15. The multi-unit air conditioner according to claim 14, wherein the float valve is arranged at a position where an associated one of the oil supplying tubes is connected with the associated compressor.
 16. The multi-unit air conditioner according to claim 13, wherein each of the adjusters comprises: an oil sensor adapted to sense an amount of oil stored in an associated one of the compressors; and a solenoid valve adapted to control supply or cut-off of the oil supplied to the associated compressor, and an amount of the supplied oil, based on the sensed oil amount.
 17. The multi-unit air conditioner according to claim 16, wherein the oil sensor is arranged in the associated compressor.
 18. The multi-unit air conditioner according to claim 16, wherein the solenoid valve is arranged at a position where an associated one of the oil supplying tubes is connected with the associated compressor.
 19. The multi-unit air conditioner according to claim 11, further comprising: strainers respectively arranged at the oil supplying tubes, and adapted to filter the oil supplied to the compressors to remove foreign matter contained in the oil.
 20. The multi-unit air conditioner according to claim 11, wherein the oil storage comprises a storing container in which a single storing chamber is defined.
 21. The multi-unit air conditioner according to claim 11, wherein the oil storage is connected with the oil separators by a plurality of oil recovering tubes, respectively.
 22. The multi-unit air conditioner according to claim 11, wherein at least one of the compressors comprises a variable-capacity compressor. 